PROJECT SUMMARY Early life perturbations, such as stress, are associated with long-term consequences on the developing brain, increasing subsequent risk of neuropsychiatric disorders that exhibit a sex bias in presentation, including schizophrenia, depression, and autism spectrum disorders. Despite advances in understanding the mechanistic roles of the maternal milieu in normal and pathological brain development, many question remain about how stress during pregnancy result in the development of offspring stress dysregulation, a pervasive symptom in neuropsychiatric disease. Recent studies indicate that maternal gut microbial communities are dynamically remodeled during pregnancy to maintain a continuous supply of nutrients to the developing fetus and prepare the mothers for the energetic demands of lactation. In our established mouse model of early prenatal stress (EPS), our preliminary studies show that newborns exposed to EPS exhibit sex-specific alterations in metabolic profiles related to energy balance and homeostasis, and, based on recent studies, may suggest that maternal changes in microbial-mediated nutrient availability may account for altered metabolite profiles in exposed offspring. Taken together, these results have led us to the hypothesis that brain development is altered by the impact of stress during pregnancy on the maternal gut microbiome and nutrient availability. Using cutting-edge `omics technologies, we aim to identify novel connections between maternal stress, the maternal gut microbiome and metabolism, and sex-specific brain development. The first aim of study will examine whether stress during pregnancy disrupts maternal gut microbiota and nutrient profiles critical for fetal brain development. This aim will utilize time-series profiling of the maternal gut microbiota, maternal peripheral metabolite and nutrient availability, and fetal brain metabolite profiles using combined metagenomics and metabolomics assessment, in addition to computational tools that integrate these datasets. As the effect of prenatal stress reprogramming on the developing brain may not emerge until later in development, the second aim will examine the lasting effect of stress on the maternal gut microbiota composition and nutrient availability on the brain development during the postnatal period. This aim will utilize time-series profiling of maternal gut microbiota, and metabolite profiles of the offspring hypothalamus using combined metagenomics and metabolomics assessment, in addition to computational tools that integrate these datasets. The final aim will determine causality of the maternal gut microbiome on brain development. Following colonization with probiotics during the window of stress exposure, then examine the impact on rescuing maternal gut microbiota composition, maternal nutrient availability, and sex-specific brain metabolite composition. Together, these studies will provide valuable insights into the mechanisms by which brain development is altered through the effect of stress on the maternal gut microbiome and nutrient availability necessary for normal neurodevelopment.